These vascular bundles have peripheral or outer phloem and inner or central xylemI. Amphicribal vascular bundles    II. Collateral vascular bundles of stemIII. Radial vascular bundles

Collateral vascular bundles of stems and amphicribal vascular bundles of pteridophytes stems have peripheral phloem and inner or central xylem. Radial vascular bundles have xylem and phloem in the same perimeter but on different radii.